270
13.
10.
27.
18.
7.
9.
8.
21.
19.for
B
D
C
AB
A
B
14.
15.
12.
11.
25.
26.
16.
17.
20.
22.
23.
24.
C
C
D
D
CMicrobiology
Study Guide
1. B
Multiple Choice
CHAPTER 5 Microbial Metabolism
Fill in the Blanks
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
precursor metabolites, energy, exergonic, release
donors, oxidation, acceptor, reduction
NAD+, NADP+, FAD
competitive, noncompetitive, competitive
respiration, fermentation
pentose phosphate pathway, Entner-Dourdoroff pathway, pyruvic acid
answers are as follows: 1) glycolysis: cytosol, cytosol; 2) Krebs cycle:
cytosol, mitochonrial matrix; 3) Electron transport chain: cytoplasmic
membrane, inner mitochondrial membrane; and 4) photosynthesis: cytoplasmic membrane invaginations called thylakoids, invaginations of the
inner chloroplast membrane which form thylakoids
protons, proton gradient, chemiosmosis
oxygen, inorganic molecules
proteases, deamination, Krebs cycle
cyclic, PSI, noncyclic, PSI, PSII
amphibolic
Matching
1.
2.
3.
4.
5.
A, B, C, D, G
A, D, F
A,E
F
B, C
6.
7.
8.
9.
10.
D, G
B,E
B
A, C, G
A, B, C, D, G
Short-Answer Questions for Thought and Review
1. Allosteric inhibition is a type of noncompetitive inhibition where regulatory
molecules bind to enzymes at sites other than the active site and turn the
enzyme off. The binding is irreversible and generally involves changing the
shape of the enzyme so that it can no longer function (cannot bind substrate). Allosteric inhibition essentially "removes" enzymes from the mix,
thus the only way to overcome the inhibition is to produce more enzyme
above the level of the inhibitor.
2. Fermentation is necessary to regenerate electron carriers (i.e., NAD+) to
keep glycolysis running. Cells that ferment can't use cellular respiration to
do this and so the only way to keep making even small amounts of energy
is to keep using glycolysis, which means you need to continually recycle the
supply of NAD+.
Answers to Study Guide Questions
271
3. Catabolism and anabolism are essentially two halves of the same coin.
Catabolism breaks down molecules into pieces that anabolism uses to
construct new macromolecules for the cell. If anabolism proceeded at a
faster rate than catabolism, eventually the anabolic systems would run out
of building blocks and the cell would stop synthesis. If the cell were
attempting to divide, it wouldn't be able to because it couldn't produce all
of the new parts it needed.
4. An example is given for step 3 of the Krebs cycle as shown in Figure 5.19.
NAD+ is the oxidized form of the electron carrier, NADH is the reduced
form. Isocitric acid and a-ketoglutaric acid are both Krebs cycle intermediates. In the equation below, the electron donor is the isocitric acid that loses
COOH in its enzymatic conversion to a-ketoglutaric acid. The hydrogen
atom is transferred to NAD+, the electron acceptor, which becomes reduced
in the process. CO2 is evolved off essentially as waste. Overall, the conversion of isocitric acid to a-ketoglutaric acid is an oxidation reaction and the
conversion of NAD+ to NADH is a reduction reaction.
Isocitric acid + NAD+ -7 a-ketoglutaric acid + NADH + CO2
Critical Thinking
1. The advantage to synthesizing everything you need from a small number of
precursors is that you are a bit less dependent on finding correct nutritional
equivalents in the environment. Such an organism can live in an environment where nutrients are not readily available or where they appear in fits
and starts. The disadvantages would include the fact that you will always
be using a lot of energy to synthesize everything, and to some extent you
will have a higher burden to keep many more metabolic pathways functioning normally. It's best to be able to do both because when nutrients are
available, you can save some energy by importing materials rather than
making them, but when the nutrients aren't there you won't starve because
you can make what you need. In this way, you can survive the variability of
the environment to a much greater extent than microbes that cannot switch
metabolic functions.
2. There are a couple of ways the cell can control amphibolic pathways. In the
case of glycolysis and gluconeogenesis, the key points where the pathway
would become dedicated to catabolism or anabolism, respectively, are
actually controlled by different enzymes. Thus if you want glucose, a
different set of enzymes is activated than if you want to break down glucose. The pathways are controlled at the point of entry. Another way such
pathways can be controlled is through the use of inhibitors and/or feedback
type situations where the products of the pathway (both catabolic and
anabolic) can be used to modulate the activity of enzymes in the pathway
to direct the pathway in one direction or another depending on need.
3. In the oxygenated environment, cellular respiration using the electron
transport chain will be the dominate energy generation mechanism. ATP is
made primarily from the proton motive force generated by the electron
transport chain. If the organism is suddenly moved to an anaerobic environment, respiration will stop once the last terminal electron acceptor
(oxygen) is used up. At this point one of two things will happen. If the cell
is capable of fermentation, it can continue to generate very small amounts
272
Study Guide for Microbiology
of ATP from the continual cycling of glycolysis, using fermentation to
regenerate NAD+. If the cell cannot ferment, and cannot use an alternate
electron acceptor, then it will most likely die.
Concept Building Questions
1. The simple answer as to why microbes can't import whole proteins inside
rather than make them is that proteins are simply too large to pass through
the outer structures microbes possess. Prokaryotes have complex cell walls
that are breached only by special channels or pores. Other microbes have
cytoplasmic membranes at the very least (some will also have other structures) that are also impassible by large proteins. Proteins cannot diffuse
through a membrane, nor are the channels, pores, or other transporters
large enough to allow such big molecules through. If they were, the holes
would be so big in the membranes of microbes that everything else could
pass in and out of the cell with little control and most likely the cell would
burst because of its inability to control movement of small molecules.
2. Enzyme-substrate complexes will be formed via weak interactions between
the two: hydrogen bonds, electrostatic associations, and some conformationally derived interactions. Essentially, those bonds that can be easily
formed and reformed will be used in the enzyme-substrate complex. Covalent bonds of any sort cannot be used to establish this complex because
they are not readily dispensable. A given enzyme may be needed to break a
covalent bond in a substrate, but it is not going to be able to work on the
substrate to the extent it needs to do that if it is itself permanently bound to
the substrate. Thus, covalent associations would prevent the enzyme from
moving the substrate, aligning it in the correct orientation, etc. In other
words, function would cease even though the enzyme would be bound to
the substrate.
CHAPTER 6 Microbial Nutrition
and Growth
Multiple Choice
1. D
6.
7.
8.
9.
D
B
D
D
11. B
16. B
12. D
17. C
18. A
10. D
15. B
2. B
3. A
4. C
5. C
Fill in the Blanks
1. nutrients
2. do, E. coli
3. nitrogen fixation
4. psychrophiles,45
5. acidophiles
6. broth, colonies
7. streak plate
8. enrichment
9.
6300+
10. turbidity, indirect
13. A
14. D